Incomplete detail provide calendar detail API with service account

Question

I am struggling with one of the Google calendar APIs. Here are the details.

Endpoint: https://www.googleapis.com/calendar/v3/calendars/<calendar_id>

Using code to call API

$access_token = "<access_token>";

$url = 'https://www.googleapis.com/calendar/v3/calendars/<calendar_id>';

$ch = curl_init();  
curl_setopt($ch, CURLOPT_URL, $url);        
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET"); 
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);   
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Authorization: Bearer '. $access_token, 'Content-Type: application/json')); 

$data = json_decode(curl_exec($ch), true);
$http_code = curl_getinfo($ch,CURLINFO_HTTP_CODE);

Which will return calendar details.

What i want: conferenceProperties with hangoutsMeet option.

-Fine with admin account: it return conferenceProperties

Api response =>
    {
            "kind": "calendar#calendar",
            "etag": "\"Oak6r8-59oLpNX7HJIoVDyu5NLA\"",
            "id": "<calendar_id>",
            "summary": "8. Liverpool Street VHT",
            "timeZone": "Europe/London",
            "conferenceProperties": {
                "allowedConferenceSolutionTypes": [
                    "hangoutsMeet"
                ]
            }
        }

-Issue with service account: this is not returning conferenceProperties which we want.

Api response => 
    {
        "kind": "calendar#calendar",
        "etag": "\"yeoDqC9bq2XMtTKibM-ToPIDR2g\"",
        "id": "<calendar_id>",
        "summary": "8. Liverpool Street VHT",
        "timeZone": "Europe/London"
    }